1. Field of the Invention
The present invention relates to a method of fabricating a CRT with a front surface having coating layers applied thereto and, more particularly, to a method of fabricating a CRT in which a silica (SiO.sub.2) coating is interposed between an anti-static layer and an anti-reflection layer, unlike a conventional fabrication where the anti-static layer is formed on the external surface of a panel by a sputtering method aid the anti-reflection layer is then formed with a sot by a spin-coating method.
2. Description of the Background Art
Normally, an anti-static coating is applied to front surface of a CRT in order to provide display device with a more comfortable feeling of sight and eliminate static electricity generated across the screen.
The reason for this is based upon a problem concerning the human body and technology, and therefore, the surface of the CRT is provided with charge and reflection protecting capabilities in order to enhance the feeling of sight and in conformity with a request for the user's convenience in use.
The construction of a CRT that meets these requirements will be described with reference to FIG. 1 as follows.
FIG. 1 is a schematic view of a conventional CRT.
As shown in the FIG. 1 a conventional CRT includes two separate panels 1 and 2. The external surface of the panel 2 is coated with an anti-static layer 3 for eliminating electric charges which are formed across the front surface of the CRT due to an applied high voltage when the user switches a PC on or off, and with an anti-reflection layer 4 for preventing an external light such as emitted from an indoor fluorescent lamp from being reflected upon the front surface of the CRT to obstruct the user's sight.
FIGS. 2(a)-(e) are diagrams illustrating a process for fabricating a wherein reference numeral 5 indicates an anti-static layer, reference numeral 6 indicates an anti-reflection layer, reference numeral 7 indicates a fixing plate, reference numeral 8 indicates a polishing machine, reference numerals 9 and 13 indicate nozzles, reference numeral 11 indicates a rotational plate, and reference numeral 14 indicates a heater or an ultraviolet lamp.
When the external surface of the panel 2 with the anti-static layer 3 and the anti-reflection layer 4, indium-tin oxide (ITO) is first applied to the surface of the panel 2 by a sputtering method, forming the anti-static lever 3.
A sol containing silica (SiO.sub.2) as a principal component is then applied to the surface of the anti-static layer 3 by a spin-coating method and the resulting material is fired (with a heat treatment), hardening the silica sol, to form the anti-reflection layer 4.
However, since indium-tin oxide (ITO) constituting the anti-static layer 3 is a metal, a problem arises in terms of adhesion between the indium-tin oxide (ITO) and the silica sol which forms the anti-reflection layer 4. This has an adverse effect upon the strength of layers.
Furthermore, if a coating is applied and fired (with a heat treatment), it is susceptible to an increase in the surface resistance.
Actually, the ITO layer has an increase in the surface resistance from 200-300 .OMEGA./cm.sup.2 (or .OMEGA./.quadrature.) to 5000 .OMEGA./.quadrature. after a heat treatment at 200.degree. C. for 30 minutes.
In other words, the surface resistance of a coating must be in a range below 10.sup.3 .OMEGA./.quadrature. so as to provide electric and magnetic fields in a monitor set, but this is not expected now to be realized in the conventional technology.
In an alternative method for forming the charge and anti-reflection layers, the front surface of a CRT is first cleaned and polished with cerox (CeO.sub.2). The polished surface is washed with purified water and alcohol and dried.
The dried CRT is placed in a pre-heater in order to heat the surface of the CRT to be coated at 40 to 50.degree. C. The front surface of the CRT is coated with a SiO.sub.2 sol containing dispersed 3-5% Sb by a spin-coating or spray-coating method, forming an anti-static layer 3, and subsequently, another silica component which differs in the refractive index from that of the anti-static layer 3 is applied to the anti-static layer 3 to form an anti-reflection layer 4 for allowing even a long term use of PCs to reduce user fatigue and do no harm to the human body.
Herein, the anti-reflection layer 4 has an uneven surface for anti-glare formed by a spray-coating method. This is to make stains caused by the anti-reflection coating invisible, thereby decreasing the diffused reflectivity, and to eliminate the problem of fingerprints left on the anti-reflection layer 4.
However, some problems that involve foreign substances arise in forming the anti-reflection layer by a spin-coating or spray-coating method, such as difficulty in removal of chemicals, increasing defects of scratches on the surface of a panel and marks of adsorption.
Such an ARAS or AGRAS coating renders the surface resistance of the AS (Anti-Static) coating layer in the range of 10.sup.7-8 .OMEGA./.quadrature. in conformity with the MPRII standard. However, this does not meet the TCO standard of most growing interest recently.
In a conventional spin(AS coating)-spin(AS coating) method, the AS layer is made of ITO which is very expensive and provides a surface resistance of 10.sup.5-6 .OMEGA./.quadrature. which is not enough to satisfy the TCO standard, and a sol used in formation of the ITO coating provides an insufficient EMI shielding effect. It is further necessary to provide a correction circuit on the monitor set in order to meet the TCO standard in which the surface resistance shall be less than 10.sup.3 .OMEGA./.quadrature..